(a) Technical Field
The present invention relates to a method and system for controlling an on-board battery charger of an eco-friendly vehicle. More particularly, the present invention relates to a method and system for controlling an on-board battery charger of an eco-friendly vehicle, which enables a charging operation of the on-board battery charger to be more smoothly performed without pause until alternating current (AC) input power is restored after instantaneous interruption of electric power.
(b) Background Art
In general, a separate on-board battery charger configured to generate a charging current for a high-voltage battery by converting external power (e.g., household AC power) into rechargeable direct-current (DC) power is mounted in a plug-in hybrid electric vehicle or an electric vehicle, which is a type of eco-friendly vehicle. Accordingly, electric energy required during driving of the eco-friendly vehicle is charged to a battery using the on-board battery charger from an external AC power source (e.g., household AC power source), thereby performing the driving of the eco-friendly vehicle.
A method for charging a battery using the on-board battery charger includes applying household AC power to the on-board battery charger mounted within a vehicle, generating a charging current by converting, AC power into DC power using the on-board battery charger, and applying the charging current generated in the on-board battery charger to a high-voltage battery to charge the high-voltage battery.
FIG. 1 is a view illustrating an on-board battery charger of an eco-friendly vehicle according to the related art and FIG. 2 is a graph illustrating a conventional charging control process of an on-board battery charger when instantaneous interruption of electric power occurs in an input power source according to the related art. The on-board battery charger is used to charge a high-voltage battery as a main battery of the eco-friendly vehicle. As shown in FIG. 1, the on-board battery charger includes a power factor corrector (PFC) converter 1, a DC-DC converter 2, a PFC controller 3, a DC-DC converter controller 8, a first capacitor 4, and a second capacitor 5.
The PFC converter 1 is connected to an output terminal of an AC power source 6 to convert an AC input voltage VAC, input from the AC power source 6, into a DC voltage VDC and simultaneously compensate a power factor of the AC power source 6. The DC-DC converter 2 is connected between an output terminal of the PFC converter 1 and an input terminal of a high-voltage battery 7 to receive a DC voltage VDC output from the PFC converter 1 and convert the DC voltage VDC into a voltage for charging the high-voltage battery 7.
In particular, an insulated DC-DC converter using a full-bridge or half-bridge type switching circuit may be used as the DC-DC converter 2. The first capacitor 4 and the second capacitor 5 are configured to constantly smooth an output voltage VDC of the PFC converter 1 and an output voltage VO of the DC-DC converter 2, respectively. The PFC controller 3 is configured to receive an AC current IAC and an AC voltage VAC, output from the AC power source 6, and an output voltage VDC of the PFC converter 1 to operate the PFC converter 1. Additionally, the DC-DC converter controller 8 is configured to receive an output current IO and an output voltage VO of the DC-DC converter 2 to operate the DC-DC converter 2.
During the charging of the on-board battery charger configured as described above, although the transmission of the AC input voltage to the on-board battery charger is stopped due to instantaneous interruption or disconnection, the controller allows the existing charging control to be maintained regardless of the on/off of AC input power. When the AC input voltage to the on-board battery charger is instantaneously interrupted, the input voltage VAC is not input to the PFC converter 1. Accordingly, the control of the PFC converter 1 is impossible due to the absence of an input voltage, and the PFC controller 3 is unable to adjust the output voltage VDC of the PFC converter 1.
Referring to FIG. 2, as a charging operation of the on-board battery charger is adjusted to be the same as the existing state (e.g., state in which the AC input voltage is on) even though the AC input voltage VAC is off, that is, as the PFC controller 3 executes a current instruction to the PFC converter 1 and a voltage instruction to the first capacitor (e.g., DC link capacitor) identically to the existing state, the output voltage VDC of the first capacitor 4 gradually decreases to be less than the minimum voltage at an AC interruption section.
In other words, in a state in which input current and input voltage of the PFC converter are absent due to instantaneous interruption of electric power, that is, in a state in which the output voltage VDC of the first capacitor 4 is not maintained at the AC interruption section, the PFC controller 3 is configured to execute the voltage instruction to the first capacitor 4, and the like to the level of the existing instruction, to gradually decrease the output voltage VDC of the first capacitor 4 to be less than the minimum voltage. Therefore, control errors of the PFC controller are continuously accumulated.
Particularly, when the AC input power is restored due to release of the interruption, a substantial AC input voltage VAC and a substantial input current IAC are instantaneously applied to the PFC converter 1 as shown in FIG. 2, and therefore, a substantial inductor current IL instantaneously flows in the PFC converter 1. Additionally, a transient voltage for recharging the battery is applied to the first capacitor 4.
When an over-voltage or over-current is repeatedly generated in the on-board battery charger due to instantaneous interruption of electric power as described above, the charging operation of the on-board battery charger mounted within the vehicle is stopped due to damage to an internal device, etc. Accordingly, when a household power source is used to charge the on-board battery charger and the AC input power source does not supply power for a few milliseconds due to instantaneous interruption of the AC input power source, the on-board battery charger continuously charges the battery by exhausting the voltage of the DC link capacitor (first capacitor 4). After that, when the AC input power is restored, a current of a few hundreds of amperes or greater instantaneously flows in the DC link capacitor to recharge the battery, and therefore, an over-voltage greater than the withstand voltage may be applied to the DC link capacitor by the current.
As a result, problems such as damage to a device due to an over-current and to a capacitor due to an over-voltage greater than the withstand voltage may occur, and therefore, the charging operation of the on-board battery charger mounted within the vehicle is stopped.